1. Field of the Invention
The present invention relates generally to methods and apparatus for generating foam, and in particular to methods and apparatus for generating foam for use in producing gypsum wallboards.
2. Description of Related Technology
Gypsum wallboard is typically produced by depositing an aqueous slurry of calcined gypsum between two continuously-supplied moving sheets of cover paper. The calcined gypsum is then allowed to set, forming a core between the two cover sheets, and the continuously-produced board may then be cut into panels of any desired length. As described for example in Johnson, U.S. Pat. No. 4,455,271, the disclosure of which is incorporated herein by reference, a gypsum board with reduced density and good board strength is typically manufactured by generating an aqueous foam in a foam generating apparatus and adding the foam to the gypsum slurry that forms the gypsum board core.
Foams for use in producing gypsum boards are typically generated in a mechanical foam generating apparatus, such as that described in U.S. Pat. No. 4,057,443, the disclosure of which is incorporated herein by reference. A foam generating apparatus typically includes an electric motor used to drive an agitator, which blends a surfactant and water to generate the foam. Consequently, a foam generating apparatus is typically expensive to operate and maintain, and includes mechanical components that are subject to wear and failure.
Static foam generating equipment, such as a cylindrical static mixer described in Johnson, U.S. Pat. No. 4,455,271 has also been used to generate foam for use in a gypsum wallboard core. The static mixer described in the Johnson patent is a six-foot-long tube packed with randomly arranged ceramic saddles in a five-foot portion of the tube and ceramic rings packed in a one-foot portion of the tube. There is a need for an improved apparatus for generating foam that is inexpensive and reliable to operate, and that consistently produces a uniform, high quality foam, which may be used to produce high quality gypsum wallboard.
According to one aspect of the present invention, a static foam generating apparatus includes a pipe having an inner diameter, an axis, an input end, and an output end. A plurality of perforated discs are disposed in the pipe, the discs positioned parallel to each other and perpendicular to the pipe axis. A plurality of spacer rings are disposed within the pipe, a spacer ring separating each perforated disc from each adjacent perforated disc.
According to another aspect of the present invention, a method for generating foam includes a step of providing a static foam generating apparatus including a pipe having an inner diameter, an axis, an input end, and an output end. The apparatus also includes a plurality of perforated discs disposed in the pipe, the discs positioned parallel to each other and perpendicular to the pipe axis. A plurality of spacer rings are disposed within the pipe, a spacer ring separating each perforated disc from each adjacent perforated disc. The method also includes the steps supplying feed water to the pipe, supplying surfactant to the pipe, and supplying air to the pipe.